The present invention relates generally to an imaging capability estimation method and apparatus for an image-formation optical system, and more particularly a method and apparatus for the estimation of the imaging capability of an image-formation optical system using a random pattern and texture analysis, yet without recourse to MTFs or test charts.
So far, MTF determination methods (e.g., patent publication 1) and methods that involves measuring resolutions from image-formation patterns on test charts (e.g., patent publication 2) have been known for the estimation of imaging capabilities of image-formation optical systems such as lens systems.
According to the method of patent publication 1, luminance distributions of edge-line images are used as estimation information to determine MTFs therefrom, and according to the method of patent publication 2, limiting resolutions of images on wedge charts are determined.
Apart from such methods, there is an MTF measurement method using a random pattern, as proposed by Sine Pattern Co., Ltd. According to this method, an image of such a two-dimensional random pattern as shown in FIG. 16(a) is formed through the image-formation optical system to be estimated to obtain such an image-formation pattern as shown in FIG. 16(b). Then, that image-formation pattern is broken down into rows and columns to obtain such row or column patterns as shown in FIGS. 16(c1) to 16(c4). An MTF is measured for each row and column, and the obtained value is squared to calculate a power spectrum density. Finally, the average value of the power spectrum density for each row and column is obtained by calculation, and the square root of that average value is taken to find MTFs in the row and column directions.
Patent Publication 1                JP(A)2001-324414        
Patent Publication 2                JP(A)2003-9190        
Non-Patent Publication 1                “Handbook for Image Analysis” compiled by the supervision of M. Takagi and one other, first edition, pp. 517-523, published on Jan. 17, 1991 from the University of Tokyo Publisher (Foundation)        
Non-Patent Publication 2                “Cyclopedia for Mathematical Information Science” by M. Oya and four others, pp. 624-627, published on Nov. 10, 1995 from Asakura Shoten Co., Ltd.        
In conventional MTF measurement methods, however, ever higher-precision measurements are imperative for correlations between visibility and MTFs, because there is no definite relation of MTFs to the visibility of an image formed through the image-formation optical system to be estimated and, hence, what difference is between them is uncertain. A drawback of how to find MTFs using a digital imaging system is that it is sensitive to image processing. Methods of finding limiting resolutions give only limiting resolutions, and render correlations with visibility vague. Another problem with the use of the digital imaging system is large errors due to position dependencies of images and pixels.